Feed the fire

Those enviable people who seem to burn off calories without effort most likely possess every weight watcher’s dream: a fast metabolism. When the body’s metabolism is working at peak efficiency, it breaks down food readily instead of storing it, thus creating abundant fuel for energy and preventing weight gain.

If your metabolism has always been sluggish or is slowing down with age, you can accelerate your internal engine by eating the right foods—including the best proteins, carbohydrates, and even fats.

Protein power Getting plenty of protein can fuel your metabolism, causing you to burn an extra 150 to 200 calories a day, says Jeff Hampl, PhD, RD, professor of nutrition at Arizona State University. “Protein is made up mainly of amino acids, which our bodies don’t store and are harder to break down [than fat and carbs], so you burn more calories getting rid of them,” he explains. But you don’t need to adopt a protein-only diet. According to the National Academy of Sciences, optimum metabolic function occurs when the body gets 10 percent to 35 percent of total daily calories from lean protein, including chicken, legumes, and soy foods. “Keep in mind, we get protein from some surprising sources, too; even green beans and carrots provide some,” Hampl says.

Low-fat dairy products are another good protein pick. Researchers recently discovered that people who drank milk or ate yogurt and cheese three to four times a day lost 70 percent more body weight than those who had less dairy intake (Obesity Research, 2004, vol. 12, no. 4). Calcium, along with other substances in dairy, tells your body to burn excess fat faster, according to study author Michael Zemel, PhD, director of the Nutrition Institute at the University of Tennessee in Knoxville. “Calcium supplements alone won’t work,” he says. “It’s the bioactive compounds in milk, yogurt, and cheese that work with calcium to produce the fat-burning effects.” Vegetarian calcium sources include broccoli and dark leafy greens, such as spinach, kale, and chard.

Burn calories with green tea Green tea appears to raise metabolic rates and speed up fat oxidation, according to clinical trials conducted at the University of Geneva, Switzerland (American Journal of Clinical Nutrition, 1999, vol. 70, no. 6). In addition to caffeine, a known metabolism stimulant, green tea contains catechin polyphenols, compounds that increase the rate at which the body burns calories. Study results were based on a daily consumption of green-tea extract containing 50 mg caffeine and 90 mg polyphenols, the amount in 2 to 3 cups of brewed tea.

—K.K.

Good carbs Carbohydrates get a bad rap from many weight watchers, but they’re important for a healthy metabolism. The key is to choose natural, complex carbohydrates, including whole fruits, vegetables, and whole grains, which take longer for your body to digest and absorb than refined carbs. This averts rapid changes in blood sugar and keeps hunger at bay. In contrast, refined starches—think white breads, rice, and pastas—are more likely to create an insulin surge that promotes fat storage and may drive down your metabolic rate, says Susan Roberts, PhD, professor of nutrition at Tufts University and author of Feeding Your Child for Lifelong Health (Bantam, 1999). “It’s important to keep carbohydrates in your overall diet, but focus on vegetables, fruits, and whole grains, including brown rice and whole-wheat pasta, which have less of an impact on insulin levels,” she says.

Healthy fats For an efficient metabolism, the amount of fat you eat is less important than the type. The worst are trans fats, contained in fried foods, margarine, and commercially baked goods made with partially hydrogenated oils. These artificial fats slow metabolism and cause your body to store fat cells instead of burning them.

Foods rich in omega-3 oils can also reduce resistance to leptin, a protein hormone that decreases the activity of enzymes which produce fat tissue in the body. Several recent reports suggest that leptin levels directly influence metabolism; in one study, University of Wisconsin and Rockefeller University researchers found that leptin-deficient mice tended towards obesity, while those with high leptin levels had faster metabolisms and burned fat more quickly (Science, 2002, vol. 297, no. 5579).

Food as fuel The bottom line for a healthy metabolism that burns calories efficiently: Eat a well-balanced diet. Choose whole grains, vegetables, and fruits. Select lean meats and low-fat dairy for protein. Always opt for healthy fats. It sounds simple, and it is. As with any fire, the fuel makes all the difference.

Kathy Kingsley is the author of The Complete Vegetarian Handbook (Chronicle, 2003) and The Big Book of Vegetarian (Chronicle, 2004).